The invention concerns a transport device, in particular for use in a vacuum chamber for the conveyance of a flat substrate through the vacuum chamber.
In the industrial processing of flat substrates, for instance when coating flat glass panes in coating facilities, preferably magnetron sputter systems, ambient conditions divergent from the ambient air must frequently be created, for example an inert gas atmosphere or a vacuum. Upstream and downstream sluice chambers or buffer chambers must be provided for this for coupling to the process vacuum in in-line inert gas chambers. The generation and relief of the vacuum in the vacuum chamber of such a magnetron sputter system should occur as rapidly as possible and the vacuum should exhibit a specified minimum degree of evacuation, in order to attain the necessary processing speed in the coating system and an economically viable coating process.
Transport devices which comprise a number of driven deflection rollers or a belt conveyor with one or more flexible infinite belts guided around at least two driven deflection rollers are usually used for conveying the substrate through the vacuum.
These transport devices exhibit dimensions in a vertical direction, which are several times the thickness dimensions of the flat substrate. The space which the deflection rollers occupy in the sluice chamber, including the unused space between them, must be completely evacuated. This space considerably increases the volume to be evacuated of the vacuum chamber. The time necessary for evacuation (generation of the vacuum) or flooding of the vacuum chamber (return of the vacuum chamber to atmospheric pressure), and, in this regard, particularly for evacuation or flooding of the sluice chambers, as well as the energy consumption required for this, therefore increase when using such a transport device. Moreover, the degree of evacuation attainable decreases with increasing volume at unchanging pump power of the vacuum pumps used.
It is therefore necessary to provide vacuum pumps with high power capacities, as the speed of the evacuation of a sluice chamber is the cycle-determining element for operation of the overall system and the process safety essentially depends on the degree of evacuation attained.
In order to reduce the time necessary for evacuation, vacuum pumps can be used with increased suction power or with the volume of the sluice chamber reduced. The reduction in the volume of the sluice chamber is, however, restricted by the above requisite dimensions of the deflection rollers. The increase in the suction power of the vacuum pump, on the other hand, leads to a higher energy consumption and is therefore not economically viable and hence undesirable.
In DE 197 14 271, a proposal was made for a reduction of the volume required by the transport device, whereby the lower strand side (26) of the infinite belt is raised to the upper strand side (18) by means of deflection rollers (24, 25) spaced closely together, while the upper strand side (18) and lower strand side (26) are guided in grooves (17) in the base wall (4) of the vacuum chamber. A drawback to this solution is the high expense for production of the base wall of the vacuum chamber and the relatively high assembly expense for the transport facility, in particular during maintenance work.